Increasing concerns regarding traditional energy sources have prompted investigation of alternative, renewable sources of energy. Energy from the power of ocean waves is a renewable energy source, from which considerable quantities of electricity can be produced.
Wave energy refers to the energy of ocean surface waves and the capture of that energy for the purpose of electricity generation. In general, the larger the wave, the more energy it contains, and therefore, the more energy that can be obtained from it. Specifically, the amount of energy which may be obtained from waves is determined by wave height, wave speed, wavelength, and water density.
Several types of wave energy conversion devices (WEC) may be used to capture wave energy. All of these devices work on a similar principle. The wave force acts on an absorbing member, which is coupled with a second member capable of relative motion to the absorbing member. The second member can also be an absorbing member. The wave force results in motion of the absorbing member relative to the second member, and the movement can be converted into electrical energy.
There are several disadvantages associated with known energy absorbing devices. Extreme waves (i.e. exceptionally large waves with respect to the average current wave state, or rapidly changing waves) can occur during otherwise benign wave states. Such large waves can cause an excessive force to be exerted on the linkage or coupling between the absorbing member and the second member. This can result in breakage of the coupling, particularly in devices with no natural damping, such as linear energy converters. Accordingly, these devices have poor survivability, even in normal wave conditions.
A further disadvantage associated with known wave energy converters is poor efficiency of energy capture. Typical devices are capable of capturing wave energy only over a relatively narrow range of wave frequencies and energy states. While more advanced devices can tune their response to enable them to optimise energy capture from any given wave state, such slow tuning usually only delivers a good response to the average power spectrum of that wave state. Few devices can respond rapidly enough to the individual frequencies within a single sea state.
There is a need for a wave energy conversion device (WEC) having damping means enabling the WEC to survive extreme waves, and also to respond rapidly to wave frequency spectrums, so as to improve survivability and/or improve the energy extraction efficiency.